Technically it may not be a primary home, but effectively it is, once on return to USA.

For an action alleging any grounds under sub section l. of section 2 [NJSA 2A;18-61.1], two months' notice prior to the institution of the action and, provided that where there is a written lease in effect no action shall be instituted until the lease expires;

Another great way is excel, its simple and effective.

I didn't do that since having a purchase contract in effect for better part of year especially when we weren't sure when they would qualify seemed "stupid." 

This was true in my case as I realized that I could find a SFR with a mother-in-law suite (tons of these in ATL) and cover my mortgage with rent from the other side.

Do some research about what is required to be disclosed in that state, especially since this effects the value of the investment.

Typically most states where you are NOT a resident only effectively tax income specifically attributable to that state in their allocation and appointment calculations. 

Even if you serve him papers, you can later drop the suit.

There are pros and cons to any style of investment and OOS suited us.

And maybe they win the suit.